Mitotic Rate is Associated with Positive Lymph Nodes in Thin Melanomas.

The American Joint Commission on Cancer will remove mitotic rate from its staging guidelines in 2018.Using a large nationally-representative cohort, we examined the association between mitotic rate and lymph node positivity among thin melanomas.149,273 thin melanomas in the National Cancer Database were examined for their association between high-risk features of mitotic rate, ulceration, and Breslow depth, with lymph node status.Among 17,204 thin melanomas with data on Breslow depth, ulceration, and mitotic rate who underwent a lymph node biopsy, there was a strong linear relationship between odds of having a positive lymph node and mitotic rate (R2 = 0.96, p <0.0001, β = 3.31). The odds of having a positive node increased by 19% with each 1-point increase in mitotic rate (Odds ratio 1.19, 95% confidence interval 1.17 - 1.21). Cases with negative nodes had a mean mitotic rate of 1.54 + 2.07 mitoses/mm2, compared to 3.30 + 3.54 mitoses/mm2 for those with positive nodes (p < 0.0001 LIMITATIONS: The data collected do not allow for survival analyses CONCLUSION: Mitotic rate was strongly associated with the odds of having a positive lymph node and should continue to be reported on pathology.